The present invention relates to optical cables and particularly, though not exclusively, to their use in way finding systems in emergency situations.
Currently available emergency way finding apparatus use lighting systems which operate by providing distributed continuous light sources. The sources are generally positioned at strategic locations such as doors, tops and bottoms of stairwells, exits etc. If a person is in unfamiliar surroundings or is disorientated, such as may happen in a smoke-filled environment, current lighting systems provide no guidance on the preferred or shortest route to safety.
Some aircraft have been fitted with strips of individual lights at floor level, these strips being set in the floor. These strips are illuminated sequentially in the event of an emergency. They are unidirectional and may, in certain circumstances, direct passengers towards rather than away from the hazard.
Side emitting optical fibres can provide light emission over a relatively long length of fibre and, in the corresponding published application WO 98/45645, a portable illumination system is described which provides light emission from a side-emitting fibre optic several kilometers in length using a laser source. Such a system has applications in emergency lighting for stairwells, cinemas, aircraft and the like. Though relatively inexpensive and portable, this illumination system is limited to illumination of a single edge emitting optical fibre which has no way finding capabilities.
Recently, electroluminescent wires have become available which provide a continuous linear light source in a flexible cable. Electroluminescent wires are available as LYTEC (Trade Mark) Electroluminescent Wires distributed by Magtech Limited, U.K. These wires require very low power to operate and hence are generally used for display purposes, e.g. Christmas tree lighting.
It is an object of at least one embodiment of the present invention to provide a directional way finding system which obviates or mitigates at least one of the aforementioned disadvantages.
This is achieved by providing a plurality of side emitting light conduits arranged side by side, and covering parts of the conduits, at repeated intervals along the length of the conduits to leave an exposed sequence of light emitting sections in each conduit, these sections being longitudinally offset in adjacent conduits, so that when the conduits are sequentially energised light is emitted from the light emitting sections to give the perception of light travelling in a forward or reverse direction (depending on how the conduits are scanned) to an observer.
According to a first aspect of the present invention there is provided a light emitting device for use in a directional way finding system said light emitting device comprising:
a plurality of side emitting light conduits arranged side by side in a longitudinal direction, each conduit having alternating optically opaque sections and light emitting sections along its length, the conduits being arranged with the light emitting sections of one conduit being offset in one direction from an adjacent conduit such that corresponding light emitting sections of the conduits form diagonal light emitting structures across the plurality of conduits at intervals along the length of the conduits.
In a preferred embodiment, the light conduits are side emitting optical fibres.
Advantageously, the light emitting device includes optical fibre positioning means, said optical fibre positioning means comprising a structure with a plurality of locating means for receiving and locating the plurality of optical fibres side by side to position optical fibre ends for illumination by a directed light beam.
The locating means may be provided by a plurality of optical fibre guide apertures disposed in said structure. Preferably the structure has first and second surfaces parallel to each other. Conveniently the plurality of optical fibre guide apertures are located between the first surface and the second surface, and are disposed in a common plane in said structure.
The optical fibre ends are located within each fibre guide aperture to align the optical fibre ends with the first surface.
Preferably the or each locating means includes securing means to secure the optical fibre in the respective optical fibre guide apertures. The securing means may be provided by a threaded aperture in which a screw is located for securing the optical fibre in the optical fibre guide aperture. Alternatively the securing means may be an adhesive material.
Conveniently, an optical component, such as a lens may be mounted within each optical fibre guide aperture near to the first surface to focus the light into the optical fibre end.
Preferably the first and second surfaces are curved. Advantageously the fibre guiding apertures are located equidistantly apart and on the same plane in said structure.
In an alternative embodiment the light conduits are side emitting electroluminescent wires.
Preferably the optically opaque sections are formed by masking a side emitting light conduit with a length of opaque material.
Advantageously the length of optically opaque material is a black plastic being heatshrunk onto the light conduit.
Alternatively the optically opaque sections are formed by positioning the light conduits in one or more partially covered receptacles. The partially covered receptacles having covered portions which are optically opaque. Advantageously the partially covered receptacles have a width approximately equal to a width of the plurality of light conduits.
Advantageously there is an equal number of optically opaque sections and light emitting sections on each light conduit.
Advantageously the optically opaque sections are longer in length than the light emitting sections.
Advantageously the optically opaque sections are twice as long as the light emitting sections.
In the preferred embodiment the optically opaque sections are one meter in length.
Advantageously the light conduits are identical.
In the preferred embodiment the side emitting optical fibres are 5 mm in diameter. In the alternative embodiment the electroluminescent wires are 2.5 mm in diameter.
Advantageously the offset is a distance substantially equal to the length of a light emitting section.
Preferably the diagonal light emitting structures across the conduits are repeated when the end of a final light emitting section of a final light conduit is substantially aligned with a start of a light emitting section of a first light conduit.
Advantageously the plurality of light conduits is up to 150 meters in length.
According to a second aspect of the present invention there is provided a directional way finding system comprising:
drive means,
a light emitting device as defined in the first aspect of the invention, and means for selectively energising one or more light conduits in a pattern to provide the perception of sequential illumination to a viewer.
Preferably the light conduits are selectively energised in a scanned pattern from a first light conduit to a final light conduit of the light emitting device to illuminate light emitting optical sections of side emitting light conduits to provide the perception of sequential illumination to a viewer.
In a preferred embodiment the drive means is a laser light source.
The laser light source may be of any type of laser but preferably is a solid state laser which is, in turn, excited by a semi-conductor diode laser.
Preferably the plurality of light conduits comprises optical fibres arranged side by side in the same plane.
More preferably there are three optical fibres.
Preferably the means for selectively energising one or more light conduits includes means for steering, in use, laser light from the laser light source to the light emitting device such that the laser light is scanned from a first optical fibre to a final optical fibre of the light emitting device to illuminate light emitting optical sections of side emitting optical fibres to provide the perception of sequential illumination to a viewer. The means for steering the laser light may be a rotatable mirror. Any suitable component which has light steering properties may be used. Preferably the mirror is mounted on a spindle which, when rotated on a vertical axis, turns the mirror and causes the laser light incident on the mirror to be reflected along the plane of the optical fibres. Alternatively the laser light is incident on the mirror to be reflected along a path which traverses a plane on a first surface of an optical fibre positioning means in which said optical fibres are disposed. The light traversing the first surface illuminates optical fibre ends located along the path.
In use the steerable optic element is rotated to scan the fibre optic ends sequentially in order from the first optical fibre to the final optical fibre or, alternatively, from the final optical fibre to the first optical fibre.
Advantageously two or more light emitting devices may be concatenated to provide a directional way finding system of an extended length. The laser light source of first light emitting device may be used as the input to one or more subsequent light emitting devices by coupling part of the laser light source output into a low-loss optical fibre, the output of this low-loss optical fibre being used as the input to a subsequent light emitting device and/or being coupled to a subsequent low-loss optical fibre. The low-loss optical fibre(s) may be positioned in parallel with the side emitting optical fibres. Coupling into and out of the low-loss optical fibre may be provided by any optical element such as a beamsplitter or lens.
In an alternative embodiment the drive means is a power supply to energise electroluminescent wires. Preferably the drive means provides a voltage of 140V a.c. 400 Hz. More preferably the drive means is derived from a 12 volt d.c. source.
Preferably the plurality of light conduits comprises electroluminescent wires arranged side by side in the same plane. More preferably there are three electroluminescent wires. Advantageously the means for selectively energising one or more light conduits includes switching means to allow selective energisation of one or more electroluminescent wires. Preferably the switching means includes a FET (Field Effect Transistor) More preferably the switching means is controlled by a microprocessor. The microprocessor may be programmed with a desired switching sequence. Advantageously the switching means and the microprocessor are isolated from each other by an opto-switch.
According to a third aspect of the present invention there is provided a method of providing an illuminated signal to provide to a viewer the perception of movement of the signal in a direction along a plurality of light conduits, said method comprising the steps of,
providing a plurality of side emitting light conduits and arranging the light conduits side by side,
masking each light conduit at repeated intervals along its length to prevent the emission of light in the masked area,
aligning corresponding masked regions in adjacent conduits to define exposed light emitting areas which have a substantially diagonal structure, and
energising the plurality of side emitting light conduits sequentially to create an emitted light signal which appears to the viewer to be travelling along the plurality of conduits in one direction.
The direction of perception in which light is travelling is selected by reversing the sequence of energising said plurality of light conduits.
In an embodiment of the present invention the method may include the step of providing sequentially scanned laser light over an extended directional way finding system by coupling a first low-loss optical fibre to the laser light source, sequentially scanning optical fibre ends of a light emitting device and energising said low-loss optical fibre to at least one subsequent light emitting device.